Ballast water is the sea water taken up and released by ships to keep their balance not to incline to one side when cargo is unloaded or loaded, or to prevent screw propeller from rising above the surface of water which makes sailing impossible. In this invention, ballast water indicates water both stored in ballast water tank (simply called ‘tank’ herein) and pumped up from the sea to store in the tank. In most cases, ballast water is sea water. According to International Maritime Organization (IMO), 3-5 billion tons of sea water is transported annually to other areas along with 7,000 species of organisms by ballasting and deballasting, which causes disturbance and even destruction of marine ecosystem.
The disturbance and destruction of marine ecosystem are not the only problem caused by ballast water. Public health is also threatened by epidemic pathogenic bacteria spread from one country to another. Such pathogenic bacteria transmitted through ballast water include microorganisms associated with waterborne disease.
Taking these matters seriously, “Ballast water Management Convention” is ready to come into effect from 2009 to intensify the supervision of ballast water. According to the “Ballast water Management Convention”, every ship that is build from 2009 is forced to equip a treatment facility for killing marine organisms (marine species) and pathogenic bacteria present in ballast water before discharging by any means, for example using a chemicals or biocides or using organisms or biological mechanisms or by altering the chemical or physical characteristics of the ballast water, etc. That is, only those ships equipped with the ballast water treatment facility or ballast water exchanging facility are allowed to sail around the world. More precisely, according to the “Ballast water Management Convention”, the amount of viable organisms of 10-50 μm in size in ballast water has to be up to 10 organisms per 1 ml for discharge and if viable organisms are as big as at least 50 μm, they has to be regulated up to 10 organisms per 1 m3. In the case of bacteria, the allowed number is similar to the number of bacteria included in the swimming beach, indicating the standard concerning bacteria is very strict. In the case of pathogenic bacteria, the allowed level is more strictly regulated, for example the number of toxicogenic Vibrio cholerae is limited to 1 cfu (colony forming unit: the number of colonies of bacteria)/100 ml, and the allowed number of intestinal Enterococci is less than 100 cfu/100 ml. The said bacteria are not the only targets of such regulation and all of pathogenic bacteria are targeted.
To meet the international standard, “Ballast Water Management Law” has been ready in Korea. According to this domestic law, it is basically prohibited for discharging ballast water in waters within the jurisdiction of Korea. It is also required to kill harmful marine organisms present in ballast water before discharging ballast water or only clean ballast water replaced in the open sea can be discharged without treatment. However, replacing ballast water with clean open-ocean water is not only inefficient but also not preferred because the population of viable organisms living in ocean water is already more than the international standard. So, this ballast water exchange is only good for temporary. Besides, replacing coastal water with open-ocean water might put a ship in danger of overturn if there is any mistake during ballast water exchange. In addition, during ballast water exchange, large area of a ship is emptied, which might result in severe default in structure or damage in the ship. Therefore, ballast water exchange in the ocean is not a preferable method.
There have been various attempts to develop methods for direct treatment of ballast water. Ballast water can be treated either before the ballast water enters the ballast tanks or before the ballast water is discharged from the ships. According to the conventional methods, sea water is pumped up and treated before being loaded in the ballast water tank. Macro-organisms present in sea water can be easily eliminated by filtration, so that most of the conventional methods use filtration to eliminate those macro-organisms. The techniques and methods under research now, therefore, target microorganisms present in ballast water, not viable macro-organisms. Thus, almost every conventional method consists of filtration for eliminating macro-organisms and sterilization for eliminating microorganisms. So, difference among the conventional methods is made by the skills to destroy microorganisms.
Chemical treatment and other methods have been developed to sterilize microorganisms.
Chemical treatment is exemplified by sterilization with hydrogen peroxide and chlorine dioxide (Korean Patent No. 10-0654105). However, using hydrogen peroxide causes acute toxicity and using chlorine dioxide causes safety problem. That is, using chemical compounds is strongly effective in treating microorganisms, particularly the effect lasts long enough since the chemical compounds remain in the tank to kill microorganisms, but these remaining chemical compounds become pollutants when ballast water is discharged out to the sea, causing a problem in maritime ecosystem.
To avoid utilizing such chemicals, alternatives have been proposed, for example a method using electrolysis that kills microorganisms with bactericides generated by electrolysis (Korean Patent No. 10-0776205 and No. 10-0597254); ozonization that kills viable organisms in ballast water by injecting ozone gas (Korean Patent Publication No. 10-2005-0104001 and No. 10-2008-0007245); UV irradiation that kills ocean microorganisms by UV irradiating (Korean Patent No. 10-0797186); high temperature treatment that kills ocean microorganisms by heating (Korean Patent Publication No. 2003-0004129); deoxygenation that kills microorganisms by making the environment not suitable for living (Korean Patent No. 10-0350409), etc. These methods have both merits and demerits. Among these methods, electrolysis and ozonization are focused. Herein, disadvantages of these methods, particularly of the above two, are explained. In the case of electrolysis, high voltage electricity is used, so that short circuit between a positive plate and a negative plate might happen and that has high risk of explosion. In addition, after long term use, various materials are accumulated on the surface of the plates, reducing the efficiency of electrolysis and requiring frequent replacement of the plates. By electrolysis, such chemicals as HOCl, NaOCl and NaOH are generated and used for sterilization but these chemicals are toxic and when they are released in the ocean, they are potentially harmful to the marine ecosystem. But, risks of these chemicals have been neglected due to the current technical limitation. In particular, the salt form of HOCl erodes the ballast water tank by forming chlorinated organic compounds. And, chlorine necessarily generated from electrolysis is another factor disturbing the maritime ecosystem. In the case of ozonization, treatment cost is high.
Electrolysis and ozonization, which do not directly use chemicals, are more pro-environmental methods than the methods using chemicals directly, but they require high price equipments and facilities, which can be a burden.
In addition to the high costs and disadvantages of each method above, the conventional methods designed not to use chemicals directly have a technical problem that is low treatment efficiency. The low efficiency problem is not only limited in electrolysis or ozonization but also observed in every conventional method developed to avoid direct chemical use. Again, almost every conventional method except direct chemical treatment has low efficiency problem. Such low efficiency is attributed to the following two reasons. One is that the conventional methods are designed to be only effective during the treatment in the inside of the equipment and they cannot give the residual effect in the ballast tanks. The other is that treatment time is too short to be efficient. According to the conventional methods designed to avoid direct chemical treatment, the treatment of ballast water is based on short-term treatment. Particularly, the conventional treatment is flow-through method and is performed during either the pumping of sea water or the discharging ballast water shortly not to delay the pumping or discharging. In reality, time cannot be waste for the ballast water treatment alone. Besides, the conventional flow-through methods are not adequate for full treatment of ballast water with enough time. Even this kind of inefficient and short conventional treatments can meet the international standard for bacteria which are regarded to be comparatively less harmful. However, they are not good enough for the treatment of pathogenic bacteria requiring more restricted standard. So, the methods capable of reducing bacteria to the required level are still insufficient for the treatment of pathogenic bacteria. Any bacteria, either general bacteria or pathogenic bacteria survived in ballast water can proliferate in the tank during sailing. Therefore, incomplete/inefficient ballast water treatment can cause a problem consequently.
To overcome this problem, alternative methods replacing the conventional methods have to be developed or methods capable of complementing the conventional methods have to be developed. The complementing method of the conventional method should be effective in the treatment of pathogenic bacteria and it is better if the method is pro-environmental.
The present inventors focused on bacteriophage capable of killing pathogenic bacteria. And the present inventors completed this invention based on the belief that bacteriophage capable of killing or reducing specific pathogenic bacteria can be a clue to develop a nature-friendly treatment method of ballast water.
Bacteriophage is a kind of virus-like microorganism infecting bacteria, which used to be called shortly ‘phage’. Bacteriophages consist of an outer protein hull enclosing genetic materials. The genetic materials are single-stranded or double-stranded DNA or RNA. Bacteriophage needs a host to grow and every bacterium has its specific bacteriophage. When a bacteriophage infects a bacterium, bacteriophage lytic protein is synthesized at the end of the multiplication cycle in bacteriophage-infected cells. This lytic protein has the ability to directly cleave the bond in the peptidoglycan layer of the bacterial cell wall; the result of this activity is degradation of the rigid murein layer and release of newly assembled virions. Bacteriophage can kill bacteria by the above procedure (Curr. Opin. Microbiol. 8: 480-487, 2005).
Bacteriophage was first found by Twort, an English bacteriologist, in 1915 while he was studying on the phenomenon that micrococcus colony was decomposed by something and became clear. In 1917, d'Herelle, a French bacteriologist, found out during filtering the feces of a patient of shigellosis that there was something capable of decomposing Shigella disentriae in the feces. Then, he further studied and found out bacteriophage. Bacteriophage means ‘eating bacteria’. Since then, bacteriophage of shigella, thypoid bacillus, and cholera bacillus have been continuously found out.
Recently, multidrug-resistant pathogenic bacteria are frequently reported because of excessive use or mis-use of antibiotics. Therefore, bacteriophage that is able to kill even multidrug-resistant pathogenic bacteria comes into the spotlight particularly in the field of medicine. Up to date, bacteriophage has been used to relieve or treat infectious disease via oral administration or injection. However, the present inventors were sure that such bacteriophage could be effectively used for eliminating or reducing pathogenic bacteria present in ballast water.
Numbers of papers and patent descriptions have been cited in this description and the citation is marked in parentheses. The descriptions of cited papers and patent documents are attached in this invention so that the art and text of this patent can be more clearly understood.